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How do you do a Bode plot comparison with LTSpice?

  1. Apr 15, 2016 #1
    I'm trying to use LTSpice in order to fine tune LC circuits, but a road block I've hit is that when I run the simulation and generate a bode plot, the previous plot is overwritten, so I can't visually compare the effects of the L C changes. Some graphing programs have a function that lets you save a plot line, so that subsequent plottings can be visually seen against a previous plot. Does LTSpice have this functionality?

    Thanks a lot!
     
  2. jcsd
  3. Apr 15, 2016 #2

    berkeman

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    Staff: Mentor

    What are you varying between your runs? Can you use the Stepping function to step component values to get all the curves on the same plot?
     
  4. Apr 15, 2016 #3
    I change the capacitance, inductance and resistances to see how it changes the Q and the resonant peak. All that is going well, it's just that short of making screen shots, I'm not sure how to compare differences from test run to test run.

    I'll looking into stepping and see if that would do it.
     
  5. Apr 15, 2016 #4
    Here's one solution I found on the 'net in case anyone comes across this in a google search:

    "I have figured out an asinine way to work around this. Put all schematics into one large schematic with all different/renamed nodes. Now all graphs can be superimposed."
     
  6. Apr 15, 2016 #5

    berkeman

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    LOL. That might work for small circuits, but not for more complex ones. Unless you're running your SPICE program on a supercomputer... :smile:
     
  7. Apr 15, 2016 #6
    Yeah, works in my case. Pretty hacky though.
     
  8. Apr 15, 2016 #7

    berkeman

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    Were you able to find the Stepping options? I use Micro-Cap, not LTSpice, so I don't know what your options are for stepping...
     
  9. Apr 15, 2016 #8

    berkeman

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    Staff: Mentor

    Also, if you are trying to optimize something, look into using the Monte Carlo features of your Spice program...
     
  10. Apr 15, 2016 #9
    Yes! In some ways that's even more convenient than what I had in mind, although it's not quite as good at "quick and dirty" comparisons, since it's more like a macro and not like a simple "screen grab". Thanks for tipping me off to that feature.
     
  11. Apr 16, 2016 #10

    donpacino

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    Gold Member

    There are also ways to run multiple simulations and change parameters with each sim.
     
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